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United States Patent |
5,549,398
|
Van Brakel
,   et al.
|
August 27, 1996
|
Bearing arrangement, roller bearings for use therein, and a method for
the manufacture of a part of the bearing arrangement
Abstract
The invention relates to a bearing arrangement and parts suitable for said
arrangement, such as a roller bearing, which is suitable for the
absorption of shock loads. To that purpose those parts which come into
contact with each other under shock loads or great loads are provided on
one of the adjacent outer contact surfaces facing each other with a
friction-reducing coating. Such a coating may contain molybdenum or bronze
and is suitably applied by means of a thermal spraying method, such as
wire spraying. The bearing arrangements provided by the invention have a
significantly longer operational life.
Inventors:
|
Van Brakel; Ronaldus J. (Driebergen, NL);
Wardle; Frank P. (Bodegraven, NL);
Verburgh; Martin (BA Amersfoort, NL)
|
Assignee:
|
SKF Industrial Trading & Development Company B.V. (NL)
|
Appl. No.:
|
285382 |
Filed:
|
August 3, 1994 |
Foreign Application Priority Data
Current U.S. Class: |
384/571; 384/492; 384/569 |
Intern'l Class: |
F16C 033/58 |
Field of Search: |
384/571,569,492,570,625,912
|
References Cited
U.S. Patent Documents
2969263 | Jan., 1961 | Lamson et al. | 384/463.
|
3853602 | Dec., 1974 | Nakamura | 117/105.
|
4511606 | Apr., 1985 | Ehrlich et al. | 427/386.
|
4714359 | Dec., 1987 | Winter et al. | 384/571.
|
5222816 | Jun., 1993 | Kondoh et al. | 384/492.
|
5375933 | Dec., 1994 | Mizutani et al. | 384/492.
|
Primary Examiner: Footland; Lenard A.
Attorney, Agent or Firm: Warnecke; Michael O., Hulseberg; Daniel J.
Mayer, Brown & Platt
Claims
We claim:
1. A bearing arrangement which is suitable for the absorption of shock
loads and is provided with parts rotating concentrically relative to each
other, which parts as a group comprise a roller bearing and further at
least a second adjacent roller bearing and/or a housing part, whereby the
parts can come into contact with each other at adjacent, facing contact
surfaces, characterized in that of at least two adjacent contact surfaces
facing each other one contact surface is coated with a friction-reducing
layer.
2. A bearing arrangement according to claim 1, characterized in that the
friction-reducing layer has a thickness 0.2 to 0.5 mm.
3. A bearing arrangement according to claim 1, characterized in that the
friction-reducing layer contains bronze.
4. A bearing arrangement according to claim 1, characterized in that the
friction-reducing layer contains molybdenum.
5. A bearing arrangement according to claim 1, characterized in that the
friction-reducing layer comprises a first and a second friction-reducing
layer in different colors.
6. A bearing arrangement according to claim 1, provided with at least one
taper roller bearing and being suitable for the absorption of axial shock
loads, characterized in that the coated contact surface is part of a
radially extending lateral surface of at least one of the parts.
7. A bearing arrangement according to claim 6, provided with two press-on
parts holding together a double taper roller bearing which has on either
side a cylindrical roller bearing, with each roller bearing comprising an
inner race ring and an outer race ring, characterized in that the inner
race ring of the double taper roller bearing has on either side of the
inner race ring radially extending lateral surfaces on the contact
surfaces coated with a friction-reducing layer.
8. A roller bearing for use in a bearing arrangement according to claim 1,
characterized in that each contact surface is coated with a
friction-reducing layer.
Description
The present invention relates to a bearing arrangement which is suitable
for the absorption of shock loads and is provided with parts rotating
concentrically relative to each other, which parts, as group, comprise a
roller bearing and further at least a second adjacent roller bearing
and/or housing part, whereby the parts can come into contact with each
other at the adjacent, facing contact surfaces.
Such a bearing arrangement is known and is applied, for instance, in a
steel-rolling mill. The bearing arrangements used therein often comprise
different roller bearings rotating concentrically and at different speeds
relative to each other. Apart from the radial forces that develop during
rolling, shock loads develop in axial direction. When, due to an axial
movement of the roller bearings, the contact surfaces of the roller
bearings contact each other, the friction occurring during slip between
the contact surfaces of the roller bearings suddenly causes a considerable
rise in temperature, which very quickly falls again as the heat is
dissipated to the roller bearings. The large and rapid fluctuations in
temperature result in a so-called "white layer" on the contact surface.
This white layer is characterized by different metallurgical properties to
those of the bearing material, which is usually steel. With time
microcracks appear at regular intervals in the contact surface, which in
time will extend into the roller bearing. This problem is described in Die
Walzlager--W. Jurgensmeyer; Berlin, publishers Julius Springer, 1937. When
microcracks have appeared in the contact surface, the roller bearing must
be replaced in order to avoid damage to the bearing arrangement resulting
in unplanned standstill of the rolling process.
It is the object of the present invention to avoid the occurrence of large
temperature fluctuations at the contact surfaces which is the cause of
microcracks, and to provide a bearing arrangement with a longer
operational life.
To that purpose the bearing arrangement according to the invention is
characterized in that of at least two adjacent, facing contact surfaces
one contact surface is coated with a friction-reducing layer.
The friction-reducing layer lengthens the time during which slip between
the contact surfaces of different roller bearings and/or housing parts
occurs, while there is less heat generation per unit of time. It takes
longer before the roller bearings have the same relative speed, allowing
for the friction heat to be removed over a longer period of time.
Consequently the temperature at the contact surface does not rise so
quickly and the occurrence of microcracks is avoided or at least delayed.
As a result the bearing arrangement has a longer operational life.
The invention further relates to a method for the manufacture of a part of
the bearing arrangement described above, whereby the part has at least one
outer contact surface.
The method according to the invention is characterized in that at least one
outer contact surface is coated by thermic spraying with a
friction-reducing layer.
Thus a friction-reducing layer is applied in an effective manner, i.e. the
layer builds up relatively quickly.
According to one preferred embodiment the friction-reducing layer is
applied by wire spraying.
This method allows the friction-reducing layer to be applied economically.
The invention further relates to a roller bearing for use in a bearing
arrangement according to the invention, which is characterized in that at
least one of its contact surfaces is coated with a friction-reducing layer
.
The invention will now be further elucidated with the aid of the drawing
illustrating one embodiment of the invention.
FIG. 1 is half of a longitudinal section of a bearing arrangement according
to the invention.
FIG. 2 shows an enlarged central part of FIG. 1.
FIG. 3a shows the temperature fluctuation near uncoated contact surfaces
resulting from axial shock loads occurring in a bearing arrangement in a
laboratory simulation, while FIGS. 3b and 3c show the effect on the
temperature when one of two contact surfaces facing each other is coated
with a bronze layer, or a molybdenum layer respectively.
FIG. 1 shows part of a bearing arrangement 1, in which reference number 2
indicates a housing to which are attached two housing parts 3 and 3' for
the purpose of keeping together the roller bearings which are described
below. Apart from seals which are not described in detail, the housing
parts 3 and 3' comprise clamping plates 4, 4' which are rotatable and are
considered to be part of the housing. The clamping plate 4, in turn, is in
contact with a roller 5. Between the clamping plates 4, 4' and the housing
2 two cylindrical roller bearings 6, 6' are positioned, and between said
cylindrical roller bearings a taper roller bearing 7 is located. The
roller bearings 6, 6' and 7 are positioned concentrically and adjacent to
each other. The cylindrical roller bearings 6, 6' comprise an inner race
ring 8 respectively 8', an outer race ring 9 respectively 9' and rotating
bodies 10 respectively 10', of which only one is shown for each
cylindrical roller bearing 6 respectively 6'. The double taper roller
bearing 7 comprises an inner race ring 11, an outer race ring 12 and
inbetween, at an angle to each other, two rows of rotating bodies 13,13'
respectively, showing one rotating body of each row of rotating bodies.
The inside diameter of the inner race rings 8, 8' and 11 are identical.
The inner race rings 8 and 11 can come into contact at the contact
surfaces 16,16' respectively and the inner race rings 11 and 8' can come
into contact at contact surfaces 17',17 respectively. In the bearing
arrangement outlined here, the contact surfaces extend radially, as shown
clearly enlarged in FIG. 2. The roller 5 has a roller shaft 14 whose
outside diameter is substantially equal to the inside diameter of the
inner race rings 8, 8' of the cylindrical roller bearings 6, 6'. At the
height of the inner race ring 11 of the double taper roller bearing 7 the
diameter of the roller shaft 14 is somewhat smaller thus forming a gap 15,
so that the inner race ring 11 cannot come into contact with the roller
shaft 14.
The bearing arrangement 1 operates as follows: the weight of the roller 5
and forces during the rolling process produce a radial load on the
cylindrical roller bearings 6, 6' exerted by the roller shaft 14. During
the rolling process also intermittent axial shock forces occur, causing
the bearing arrangement 1 to be loaded in an axial direction. These forces
must not be absorbed by the cylindrical roller bearings 6, 6', as this
could damage the cylindrical roller bearings, but must be passed on to and
absorbed by the taper roller bearing 7. This occurs as follows. An axial
force towards the bearing arrangement, produced during the rolling
process, is transmitted by the roller 5 via the clamping plate 4 to the
inner race ring 8 of the cylindrical roller bearing 6. Because of the
axial clearance in the cylindrical roller bearing 6 this is not loaded,
and the contact surface 16 of the inner race ring 8 transmits the force
via contact surface 16' to the inner race ring bearing 11. Via the conical
rotating body 13', the outer race ring 12 of the taper roller bearing 7
and the outer race ring 9' of the cylindrical roller bearing 6' the force
is transmitted to the housing 2 via housing part 3'. Because of the
afore-mentioned axial clearance none of the cylindrical roller bearings 6,
6' is subjected to axial forces which are damaging to the bearing. The
smaller diameter of the roller shaft 14 at the height of the taper roller
bearing 7 ensures that the roller shaft 14 is not in contact with the
inner race ring 11 of the taper roller bearing 7. As a result the taper
roller bearing 7 is not loaded in axial direction. Consequently, without
axial load, the inner race ring 11 will come to a halt due to contact with
the stationary housing 2 via conical rotating bodies 13, 13' and the
rotatable outer race ring 12, as opposed to the inner race rings 8, 8' of
the radially loaded cylindrical roller bearings 6,6'. The axial force
causes the contact surfaces 16, 16' of the inner race ring 8 of the
cylindrical roller bearing 6, and the inner race ring 11 of the taper
roller bearing 7 respectively, to come into contact with each other. The
big difference in speed causes slip between the contact surface 16 of the
rotating inner race ring 8 and the contact surface 16' of the not at all
or much more slowly rotating inner race ring 11, whereby short temperature
fluctuations occur with detrimental effects for the material properties on
the contact surfaces 16, 16' of the respective inner race rings 8 and 11.
According to the invention, one of the contact surfaces of the facing
contact surfaces 16, 16' (respectively 17', 17) of the inner race rings 8
and 11 (respectively 11 and 8') is provided with a friction-reducing
layer.
In the case of axial loading, the contact surface of the uncoated inner
race ring, usually made of steel, comes into contact with the
friction-reducing layer of the contact surface of the coated inner race
ring. With the coated contact surface according to the invention, the
occurrence of undesired metallurgical changes such as the formation of a
white layer and the development of microcracks, is avoided or at least
delayed.
The friction-reducing layer may be applied by thermal spraying, such as
plasma spraying or wire spraying. Wire spraying is preferable to other
spraying methods. The material applied by means of thermal spraying is
preferably bronze or molybdenum. The method of wire spraying of bronze and
molybdenum is known to the expert. Wire spraying involves a work gas flow
which is preferably air. In this way a bronze or molybdenum layer applied
by wire spraying has a certain oxygen content. Oxygen-containing bronze
and molybdenum layers applied in this way proved to be very suitable.
In order to examine the effect of the friction reducing layer according to
the invention, the occurrence of slip as a result of an axial shock load
was simulated in a laboratory setting. To this end two concentric outer
rings of the same size were rotated at a speed of 2058 rpm, while an inner
ring, not in contact with these two outer rings, concentrically placed
between them and of the same size, did not rotate. Then by means of a
hydraulic system the two outer rings were pressed against the inner ring
with a force of 825 N. This process was repeated, whereby the force was
applied for 5 seconds and subsequently removed for 30 seconds. The
temperature was measured as close to the contact surfaces as possible
between an outer ring and the inner ring. It will be appreciated that at
the actual contact surfaces much higher temperatures are reached,
affecting the material properties of the contact surfaces. Measuring the
temperatures at the actual contact surfaces is very difficult, while
taking measurements near the contact surfaces is much simpler and yet
gives sufficient indication for the temperatures occurring at the contact
surfaces. In FIG. 3a the temperature variations for uncoated rings, as
well as the torque measured with the aid of a sensor, are plotted as a
function of the number of revolutions of the outer rings. It can be seen
that the temperature fluctuates between about 60.degree. and 130.degree.
C. The torque, which is a measure of the amount of friction, is about 20
Nm. After about 67,000 revolutions a white layer developed followed by the
formation of microcracks. The experiment was then stopped.
In concurrence with the invention the contact surfaces of the inner ring
were provided with a 0.5 mm thick layer of molybdenum (FIG. 3b) or bronze
(FIG. 3c) applied by wire spraying. Thereupon about 0.1 mm were turned
off, leaving a layer having a thickness of about 0.3 to 0.4 mm.
The temperature variations represented in FIG. 3b for a contact surface
coated with molybdenum show that there is much less temperature
fluctuation, particularly at the beginning, and that less high
temperatures are reached. Ultimately the temperature varies in the range
of 60.degree. to about 110.degree. C. After roughly 430,000 revolutions
the molybdenum layer has practically disappeared and the torque has
reached a value of about 20 Nm. Compared with the uncoated inner rings
from the experiment described above, the rings of which one contact
surface is coated with molybdenum, last about 6 times longer.
FIG. 3c shows the temperature variations in an inner ring coated with
bronze (Sprabronze AA). For 1.2 million revolutions the temperature
fluctuates between about 45.degree. and 85.degree. C. The torque clearly
lies below 20 Nm, even toward the end of the experiment, when the bronze
coating has nearly completely disappeared. On average, when one contact
surface of the rings is coated with bronze, they last 20 times longer than
when the rings are uncoated.
These examples show that by applying a friction-reducing layer according to
the invention, the extent of the temperature fluctuation is decreased and
problematic high values are reached only much later. The life of the
rings, that is to say until a white layer has formed and microcracks
develop, is greatly extended, especially when bronze is used as coating
material. The following Table shows the average life of the rings.
______________________________________
Layer life in rpm
bronze 1,400,000
molybdenum 420,000
uncoated 70,000
______________________________________
In general the thickness of the friction-reducing layer is 0.1 to 1 mm,
depending on the material that is used. Layers between 0.2 and 0.5 mm are
preferred.
The friction-reducing layer will wear off during operation of the bearing
arrangement, and in order get an indication of this, the friction-reducing
layer may comprise a first and a second friction-reducing layer in
different colours. To this end the inner race ring may first be provided
with a thin layer of molybdenum followed by a thicker layer of bronze.
When through wear the molybdenum layer becomes visible, the bearing must
be replaced, which will happen before the bearing is damaged. As the
bearing has remained undamaged, it is possible to provide the particular
bearing part with a new friction-reducing layer, whereby remnants of a
previous friction-reducing layer can be removed before coating the contact
surface.
The invention is neither limited to the embodiments of bearing arrangements
applied in the steel industry nor to the prevention of problems caused by
axial shock loads.
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